Method for producing sodium borates of lowered iron content



. 3,800,700 METHOD FOR PRODUCING SODIUM BORATES F LCWERED IRON CONTENT George W. Campbell, Jr, Santa Ana, Calif., assignor to United States Borax & Chemical Corporation, Los

Angeles, Calif., a corporation of Nevada No Drawing. Filed May 13, 1960, Ser. No. 28,819

4 Claims. (Cl. 23-59) The present invention relates as indicated to a method for producing sodium borates of lowered iron content.

Most commercial sodium borates as, for example, sodium tetraborate decahydrate and sodium tetraborate pentahydrate are produced from ores containing the crude borates combined with a gangue comprising clay and small amounts of various impurities.

The common method for the recovery of the sodium borates is a wet process in which the ore is treated in a dissolving tank with water or a mother liquor containing sodium borate in solution. The sodium borate is dissolved in the water or mother liquor and separated from the gangue by subsequent screening, settling and filtration. The finished sodium borate products are then usually obtained from the clarified solution by crystallization. The clarified sodium borate solutions before crystallization contain on the order of about 25 parts per million total iron and the finished products when crystallized from these solutions contain on the order of about 15 parts per million total iron. For most of the commercial uses of the sodium borates this small quantity of iron is of no importance; however, there are various requirements for sodium borates wherein it is necessary that the iron content be on the order of 8 parts per million and less.

It is, therefore, the principal object of the present invention to provide a wet process for producing sodium borates having a lowered iron content.

Other objects of the present invention will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, said invention then comprises the features hereinafter fully described and particularly pointed out in the ciairns, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

Broadly stated, the present invention comprises the method of producing sodium borates having a lowered iron content which comprises contacting an aqueous solution of sodium borate having a pH of at least 8.5 and containing iron as a contaminant with a metal selected from the group consisting of zinc, aluminum, magnesium and manganese, displacing the iron from said solution with said metal and crystallizing sodium borate substantially free of iron from said solution.

The foregoing broadly stated paragraph presents a process for lowering the iron content of sodium borates which is contrary to accepted electrochemistry. The sodium borate solutions which are treated are aqueous solu tions and due to this fact, substantially unlimited quantities of hydrogen ions are available, and the following series of mathematical equations, derived from the teachings of the prior art, show that hydrogen rather than iron should be eliminated from the sodium borate solutions when contacted with zinc, aluminum, magnesium or manganese, especially when the iron concentration of the sodium borate solution is about 20 parts per million or less.

The following mathematical equations are calculated using the Nernst equation. The Nernst equation and its use in determining electrode potentials can be found in concentration of 20 parts per million.

20X1XL2X10 a 106x559 4.3)(10 Molar 2O p.p.m. (Fe

log (Fe+ log (4.3)( 10') E, 0.540v. Equation2: Concentration of Fe++=5 p'.p.m.

5 (FEM) 10 x559 =1.1 10- Molar 0.0g915 10g (Few) Equation 3: pH of solution=8.5. Pressure of hydrogen =1 atmosphere.

Equation 1 gives the electrode potential of iron at a A 20 part per million iron concentration was chosen as this is a representative starting concentration for iron in sodium borate solutions. I

Equation 2 gives the electrode potential of iron at a concentration of 5 parts per million. The 5 parts per million iron concentration was chosen for comparison with the 20 parts per million concentration and to point out that the tendency for hydrogen rather than iron to be displaced should increase as the iron concentration is lowered.

Equation 3 gives the electrode potential of hydrogen in a solution having a pH of 8.5. A pH of 8.5 was chosen because the sodium borate solutions prepared in the present invention have a pH range on the order of from about 8.5 to 9.5, and a pH of 8.5 is most detrimentel no the displacement of iron by an active metal such as zinc, aluminum, magnesium and manganese.

According to accepted principles of electrochemistry the element in a solution having the lower electrode potenti-al is displaced prior to the element having the higher electrode potential when contacted with an active metal. It has been shown that in an aqueous sodium borate solution, hydrogen has an electrode potential of from about 0.037 volt to about 0.054 volt lower than that of iron and should therefore be displaced'prior to the disswoaroo 3 placement of iron by an active metal. It is to be noted here that although the diiference in electrode potential of hydrogen and iron seems slight, many electrolytic processes are based on such difierences.

"The reasons why iron is displaced from an aqueous sodium borate solution prior to the displacement of hydrogen by an active metal are not fully understood; however, the fact remains that I have successfully produced sodium borate having lowered iron content by the present method.

I have found that iron can be removed from both clarified and unclarified sodium horate solutions by" con tact with zinc, aluminum, magnesium or manganese. The sodium borate solution may be contacted with large solid pieces of these metals in a holding tank for a period of from about 3 to 6 hours to lower the iron content from about -25 parts per million downto about 2; to 8 parts per million. When speed of reaction is desired a large surface area of metal is needed and small pieces of metal, such as turnings or granules havinga pa'rticle size of one mesh or less or even powdered metal, may be introduced into the solution and the desired end results may be reached in much shorter periods of time.

So that the present invention is more clearly under stood,.the following examples are given tor illustrative purposes: I

A sodium borate solution containing gangue and 22.1 parts per million iron was placed in a holding tank. Several pieces of mossy zinc were suspended in the solution for a period of five hours. The solution was then sampled and chemical analysis yielded the following data:

Iron content after five hours-7.9 parts per million.

III

A clarified sodium bot-ate solution containing 19.9 parts per million iron was treated with mesh granules of aluminum. After 30 minutes the remaining aluminum particles were removed from the solution by filtration and the solution was sampled. Chemical analysis yielded the following data:

- Iron content after 30 minutes-7.1 parts per million.

1V A sodium borate solution containing 'gangue and 19.4' parts per million iron was placed in a holding tank. Sev- A clarified sodium borate solution containing 20.1 parts per million iron was placed in a holding tank. Several large pieces of manganese were added to this solution and after four hours the solution was sampled. Chemical analysis yielded the following data:

Iron content after four hours3.4 parts per million.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described provided the features stated in any of the following claims or the equivalent of suchv be employed.

I, therefore, particularly point out and distinctly claim as my invention: r

1. The method of producing sodium borates having a lowered iron content. which comprises contacting an aquecos I solution of sodium horate having a pH of at least 8.5 and containing iron as a contaminant with a metal selected from the group consisting of zinc, aluminum, magnesium. and manganese, and crystallizing substantially iron-free sodium borate from said solution.

2. The method of producing sodium borates having a lowered iron content which comprises contacting an aque onev sodium borate solution having a pH. range of from about 8.5 to about 9.5 and containing iron as a contaminant' with a metal selected from the group consisting of zinc, aluminum, magnesium and manganese, and crystallizing substantially iron-free sodium borate from said solution.

3. The method of claim 2 wherein said metal used is 4. The method of claim 2 wherein said metal used is aluminum.

References Cited in the file of this. patent 555,090 Canada Mar. 25, 1958 

1. THE METHOD OF PRODUCING SODIUM BORATES HAVING A LOWERED IRON CONTENT WHICH COMPRISES CONTACTING AN AQUEOUS SOLUTION OF SODIUM BORATE HAVING A PH OF AT LEAST 8.5 AND CONTAINING IRON AS A CONTAMINANT WITH A METAL SELECTED FROM THE GROUP CONSISTING OF ZINC, ALUMINUM, MAGNESIUM AND MANGANESE, AND CRYSTALLIZING SUBSTANTIALLY IRON-FREE SODIUM BORATE FROM SAID SOLUTION. 